As you can see, it’s basically a special bike path that exists a little higher than street level and a little lower than the sidewalk. The SF Bike Coalition reports:

The showcase bikeway is part of the Mission/Valencia Gateway project and will stretch southbound on Valencia Street from Cesar Chavez Street to Duncan Street.

[...]

Work on the project is scheduled to begin in the first quarter of 2015 and continue until mid-2016. When completed, the Mission Valencia Green Gateway will create an improved link between the Valencia and San José corridors, making the North to South Connecting the City route even safer and more comfortable for everyone.